1. Field of the Invention
The present invention relates to a compound semiconductor light emitting device and a method for manufacturing the same; and, more particularly, to a compound semiconductor light emitting device including a protection layer on the surface of a Si—Al substrate, and a method for manufacturing the same.
2. Description of the Related Art
A GaN-based semiconductor, which is expressed as AlxGayIn(1-x-y)N (0≦x≦1, 0≦y≦1, 0≦x+y≦1), has been used for a blue or green LED (Light Emitting Diode) as a compound semiconductor appropriate for light emission in blue and ultraviolet regions. A generally used GaN-based LED includes an n-type GaN-based semiconductor layer, an active layer, a p-type GaN-based semiconductor layer and two electrodes (n-side electrode and p-side electrode) which are sequentially grown on a sapphire substrate. Since the sapphire substrate used as a growth substrate is made of insulating material, the two electrodes are horizontally arranged.
Since in the GaN-based LED having such a horizontal structure, both of the two electrodes are positioned at an upper part of the LED, the LED should have a wide area. In addition, a transparent electrode for current spreading and the n-side electrode are disposed close to each other, which makes the LED vulnerable to defect caused by static electricity.
Instead of the GaN-based LED with the horizontal structure having the disadvantage, a vertical GaN-based LED is recently used which uses a conductive SiC substrate as a growth substrate of a GaN-based semiconductor. However, this has a disadvantage in that the high-cost SiC substrate is used.
Another vertical GaN-based LED is manufactured through a bonding process of a conductive substrate and a separation process of a sapphire substrate. For example, Korean Patent Laid-open Publication No. 10-2004-0058479 discloses a vertical GaN-based LED including a conductive substrate such as an Si substrate bonded to a GaN-based semiconductor layer by a conductive adhesion layer.
However, in the case of the conventional vertical GaN-based LED manufactured through the bonding process of the conductive substrate such as the Si substrate and the separation process of the sapphire substrate, there is caused a defect such as a crack in the GaN-based semiconductor layer when separating the sapphire substrate through laser irradiation. This is because CTE (Coefficient of Thermal Expansion) (approximately 2.6 ppm/K) of Si that is material of the conductive substrate is much lower than CTE (6 to 7 ppm/K) of the sapphire substrate.
More specifically, if the conductive substrate made of Si is bonded to the GaN-based semiconductor layer at a temperature of approximately 200 to 400° C. and then cooled at a room temperature, the conductive substrate contracts slightly, while the sapphire substrate contracts considerably. As a result, a large tensile stress is applied to the sapphire substrate to thereby warp the conductive substrate and the sapphire substrate. If the sapphire substrate is separated through laser irradiation in a warped state due to the tensile stress, mechanical impact is applied to an interface between the sapphire substrate and the GaN-based semiconductor layer to thereby cause a lot of cracks in the GaN-based semiconductor layer.
Therefore, an Si—Al substrate having a similar CTE to that of the sapphire substrate is recently used instead of the Si substrate as the conductive substrate, thereby obtaining a high-quality vertical semiconductor light emitting device which reduces the generation of crack.
However, in the case when the Si—Al substrate is used, Al of the Si—Al substrate is easily etched due to attack of chemicals such as acid and alkali used in a process of manufacturing a light emitting device to thereby generate severe unevenness on the surface of the Si—Al substrate, which causes an error that the GaN-based semiconductor layer is peeling off which is bonded to the Si—Al substrate.